Riverdale Public Consultation - May 14, 2015

River Valley Neighbourhoods Flood Risk Study

1. Provide results of the studies done regarding drainage issues in your neighbourhood.

2. Discuss proposed flood mitigation improvements.

3. Share Drainage Services’ process for moving improvements forward.

4. Outline next steps. 5. Answer questions/get your input and

feedback.

Today’s Meeting

After Today’s Meeting

1. Summarize and share meeting input. 2. Consider community input in work ahead. 3. Report on progress and keep you informed.

Please hold questions until after presentation.

Study Objectives

1. Comprehensive review and understanding of the existing drainage and sewer systems. ● Cloverdale ● Riverdale ● Rossdale

2. Develop flood mitigation concepts to improve the level of flood protection in the neighbourhoods.

What is a 100 Year Event?

Return Period % Chance of Exceedance in any given year

100 year 1% (1/100) 50 year 2% 25 year 4% 10 year 10% 5 year 20% 2 year 50%

A 100 year event has a 1% chance of being exceeded in any given year.

North Saskatchewan River

● River flows

recorded since 1911(104 years)

● The dams have

negligible impact on extreme peak flows events.

Brazeau Dam (1960)

Bighorn Dam (1971)

City of Edmonton

0

1

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612

613

614

615

616

617

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619

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625

2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 200-yr

Wat

er D

epth

(m)

Wat

er E

leva

tion

at L

ow L

evel

Brid

ge (m

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Return Period

June 2013

North Saskatchewan River Water Levels

June 1915

July 1986

Today

June 2011

Floodplain Mapping

Note: This map shows the area on the ground surface that will be flooded due to high River water levels. It does not show properties that may experience sewer backups or underground parking floods.

Existing Drainage and Sewer System

First combined sewers in Riverdale installed in 1910. Most were replaced/rehabilitated since then. The latest combined sewer upgrades were implemented in 1997/98. No flows from other neighbourhoods.

Existing Drainage and Sewer System

Riverdale Pump Station was constructed in 1958; most recent upgrades in 2007. In 1998, a 1800mm diameter storage tunnel (460m3 storage) was constructed near the pump station.

Pump Station

Storage Tunnel

Existing Drainage and Sewer System

In 1997/98, the City constructed several storm sewers with new outfalls. Almost all of the catchbasins in Riverdale are connected to the storm sewer system.

Existing Drainage and Sewer System

2001: Brickyard Development. Sanitary sewers connected to existing combined sewer system. Storm Sewers connected to storm outfalls.

Main Drainage Issues Intense Rainfall

1- A few catchbasins are still connected to the combined sewers..….............Risk of Sewer Backup (localized) 2- Several homes have roof leaders connected to the combined sewers…….Risk of Sewer Backup (localized) 3- Large ponding area in localized areas threatening to flood homes.…........Risk of Surface Floods (localized)

Main Drainage Issues High River Water Level

1- Few catchbasins connected to combined sewers are in floodplain….....Risk of Sewer Backup (widespread) 2- High River may backflow into storage tunnel and pump station………...Risk of Sewer Backup (widespread) 3- High River Water Levels flooding floodplain (>1:10 year).……………….. Risk of Surface Floods (floodplain)

Main Drainage Issues Top 5 Concerns According to Residents

1. High River water levels overflowing banks and flooding homes located near the River.

2. Erosion of the River banks. 3. Sump pumps discharging to ground forming ice on

sidewalks during winter. 4. Storm drains clogged by leaves and snow causing

street flooding. 5. Concerns about infill development creating additional

sewer flows.

Improvements Concepts

Main Objectives ● Increase the level of flood protection, and

reduce flood risks throughout Riverdale due to: ● Intense Rainfall ● High River Water Level ● Both at the same time

● Provide up to 100 year level of flood protection

Improvements Concepts Intense Rainfalls

1. Provide additional sewer separation (catchbasin reconnections, new storm sewers) 2. Roof leader disconnection from combined sewer pipes at select locations. 3. Provide drainage and storm sewer improvements (e.g. new sewers, additional catchbasins, swales)

1. Prevent River water from entering the sewer system via the outfall (at pump station storage) 2. Prevent River overflow from entering into the sewer system via the manholes (manhole sealing) 3. Catchbasin reconnection to storm sewer system (if located in floodplain).

Improvements Concepts High River Water Level – Sewer Backups

Improvements Concepts High River Water Level – Surface Floods

● Current Strategy: ● Flood proofing of homes – by homeowner. ● City installs sand bags at most vulnerable properties.

● Alternative Solutions:

● Permanent Flood Barrier (i.e. berm, wall) along River. ● Temporary Flood Barrier installed days before floods

and removed after flood. ● Flood barrier: Up to 3.8m high, 1000m in length.

Improvement Concepts High River Water Level – Surface Floods

● Alberta Government conducting Flood Study on

North Saskatchewan River watershed. ● Expected completion in 2015.

● Work with the Alberta Government to identify

next steps and develop a flood mitigation plan.

Improvement Concepts Enhanced Communications

● Provide early warning system for the residents when: ● High River water levels that may cause flooding is forecasted.

● Implement Communication Plan:

● Email List ● Community League ● Street Signage ● Social Media

Until improvements are in place, what can residents do to prevent flooding?

Physical Improvements: 1. Install backflow valve on the sanitary service line to reduce

the risk of sewer backups in basement. a) Drainage Services has a Backflow Valve Subsidy Program.

2. Ensure roof leaders discharge to ground surface. 3. Ensure lot grading is sloped away from your home. 4. Install weeping tiles, connected to a sump and sump pump. 5. Ensure sump pump discharges on ground or into storm sewer.

City of Edmonton’s Flood Prevention Home Check-Up * Free Inspection and Recommendations by Drainage Specialist *

Prior to High River Water Level / Intense Rainfall: 1. Move valuables to high ground (not basement). 2. Ensure street catchbasins are free of debris. 3. Ensure eavestroughs are clean. 4. Park vehicles at safe location:

a) Not in depressions on the streets. b) Not in underground garage. c) Not in floodplain.

5. Minimize water usage.

Until improvements are in place, what can residents do to prevent flooding?

Planning (Study, Analysis,

Concept Projects, Community Input, and

Validation)

Budgeting (Business Case,

Funding Opportunity and Reviews)

Pre-design, Design,

Construction

Operation and

Maintenance

Now

Next Step

Next Steps

TBD

On-going

1. Implement immediate improvements: a. Improve communication during a potential flooding threat from high

river levels.

2. Take input, validate and prioritize recommended improvements.

3. Look at how high priority projects can be advanced as quickly as possible.

Next Steps

4. Coordinate planning and work with: a. Drainage Services programs including Neighbourhood Renewal

Program, Opportunistic Sewer Separation, Flood Mitigation Program and Sewer Upgrading Strategy.

b. Other City departments like Transportation. c. Other organizations like Community League.

5. Follow up with provincial North Saskatchewan River Basin Study.

6. Support homeowners via Flood Prevention Home Check-up and subsidies.

Next Steps

Questions Comments